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Data Communications
Data Communications
Data Communication is the exchange of data (in the form of 0โs and 1โs) between two devices via some form of transmission medium (such a cable)
What is important?
โฆ (^) Delivery (deliver data to the correct destination) โฆ (^) Accuracy (must deliver the data accurately, no altered data in transmission) โฆ (^) Timeliness (deliver data in timely manner, data delivered late are useless)
Aspects of Data
Communications
Components
Data representation
Direction of data flow
Components (contd.)
Components of a Communication System
Message : The message is the information (or data) to be transmitted. For example, text, numbers, pictures, sound, video, or any combination of these. Sender : The sender is the device that sends the data message.It can be a computer, telephone, video camera, and so on. Receiver : The receiver is the device that receives the message. Medium (Channel) : The transmission medium is the physical path by which a message travels from the sender to receiver. For example twisted pair wire, coaxial cable, fiber-optic cable, radio waves (terrestrial or satellite microwaves).
Components (contd.)
Protocol: A protocol is a set of rules that govern data communication. It represents an agreement between the communicating devices.
Direction of Data Flow
Simple x Half-duplex Full-duplex
Networking
Network
A network is a set of devices (often referred to as nodes) connected by links. A node can be a computer, printer, or any other device capable of sending and/or receiving data generated by other nodes on the network.
Network criteria
โฆ (^) Performance โฆ (^) reliability โฆ (^) security
Multi-point Connection A multipoint line configuration is one in which more than two specific devices share a single link. In a multipoint environment, the capacity of the channel is shared, either spatially or temporally.
Physical Topologies The topology of a network is the geometric representation of the relationship of all links and linking devices to one other. Two or more devices connect to a link; two or more links form a topology.
Mesh Topology (contd.)
Advantages
The use of a dedicated links guarantees that each connection can carry its own load, thus eliminating the traffic problems that can occur when links must be shared by multiple devices. A mesh topology is robust. If one link becomes unusable, it does not incapacitate the entire system. Privacy. When every message sent travels along a dedicated link, only the intended recipient sees it. Physical boundaries prevent other users from gaining access to messages. Point-to Point links make fault identification and fault isolation easy.
Mesh Topology (contd.)
Disadvantages
A big amount of cabling and a big number of I/O ports required, i.e, the hardware required can be very expensive. Because every device must be connected to every other device, installation and reconfiguration are difficult. For these reasons a mesh topology is usually implemented in a limited fashion. For example, as a backbone connecting the main computers to a hybrid network that can include several other topologies.
Star Topology (contd.)
Advantages
It is easy to install and reconfigure The star topology is robust. If one link fails, only that link is affected. This factor also lends itself to easy fault identification and fault isolation.
Disadvantages
A big amount of cabling and a big number of I/O ports required, i.e, the hardware required can be very expensive. Note: Star topology requires far less cable than Mesh topology.
Bus Topology (contd.)
Advantages
Easy to install Bus topology uses less cabling than mesh, star, or tree topologies.
Disadvantages
Difficult reconfiguration and fault isolation. A bus is usually designed to be optimally efficient at installation. It can therefore be difficult to add a new devices. A fault or break in the bus cable stops all transmission, even between devices on the same side of the problem. The damaged area reflects signals back in the direction of origin, creating noise in both directions.
Ring Topology (contd.)
Advantages
Easy to install and reconfigure. To add or delete a device require only two connections. Easy fault isolation
Disadvantages
A break in the ring (such as a disabled station) can disable the entire network.
Categories of Networks
